The present invention relates to a hermetic motor compressor suitable for use for the compression of refrigerant in air conditioners and refrigerators.
Air conditioners or refrigerators incorporate a closed refrigerant circuit constituted by a refrigerant compressor, condenser, pressure reducer and an evaporator which are connected in series by refrigerant pipes.
The compressed refrigerant gas discharged from the refrigerant compressor is cooled and liquefied in the condenser, and the liquefied refrigerant flows, after a pressure reduction by the pressure reducer, to the evaporator. The liquid refrigerant of lowered pressure is evaporated in the evaporator through heat absorption from a fluid which serves as a cooling object, to become gaseous refrigerant which then is recycled to the refrigerant compressor thus completing one cycle of operation. The fluid serving as the cooling object is cooled in the evaporator through heat exchange with the refrigerant, and is forwarded for the purpose of air conditioning or refrigeration.
The use of a hermetic motor compressor as the refrigerant compressor has become popular. The hermetic motor compressor has a closed housing in which a motor section and a compressor section are assembled as a unit.
The compressor section has a cylinder formed integrally with the frame. A cylinder head provided at one end of the cylinder has a suction valve and a discharge valve. A head cover is disposed at the outside of the cylinder head. A suction chamber and a discharge chamber are formed in the head cover. A vertical suction pipe provided in the suction chamber extends to open at an upper part of the space within the closed housing. The cylinder accomodates a piston adapted to make a reciprocatory motion therein. The piston is connected to a crank shaft through a connecting rod.
The motor section has a stator fixed to a plurality of supporting posts provided around the frame, and a rotor disposed at the inside of the stator and coupled to a motor shaft which is integral with the crank shaft.
In operation, the refrigerant gas is sucked into the closed housing through a return pipe connected to the latter, and is sucked into the suction chamber formed in the head cover. The refrigerant gas is then sucked into the cylinder by forcibly opening the suction valve due to the pressure differential across the latter.
The refrigerant gas sucked into the cylinder is compressed by the reciprocating piston and is discharged to the discharge chamber in the head cover by forcibly opening the discharge valve. The compressed refrigerant gas is then delivered to the outside of the motor compressor through the discharge pipe and a discharge silencer.
The sliding parts of the motor compressor are lubricated and cooled by lubricant sucked up from an oil storage pan formed at the bottom of the closed housing.
To explain the construction of the head cover in more detail, the discharge portion is formed in the extension of the cylinder, and the suction chamber is formed therearound. The outside dimensions of the head cover is determined by the size of the frame constituting the cylinder. In addition, since the discharge valve portion has a diameter smaller than that of the cylinder, the suction chamber formed in the head cover is made to have a comparatively large volume.
The hermetic motor compressor having the described construction is incorporated in the closed loop of refrigerant circuit. If this hermetic motor compressor has a temperature lower than those of other constituents of the refrigerant circuit, or if the same is located at a height below other constituents, the refrigerant of the refrigerant circuit concentrates at the closed housing of the motor compressor during suspension of operation, and is liquefied to be mixed with refrigerator oil in the housing.
The head cover and other associated members, made of metallic materials, have large heat capacity so that the gaseous refrigerant therearound is liquefied to become liquid refrigerant due to a heat absorption by these metallic parts. The refrigerant liquefied in the head cover is collected at the lower part of the suction chamber. Since the suction chamber has a large space as mentioned before, the area of the inner surface of the suction chamber is correspondingly large, so that a large amount of refrigerant is liquefied in the suction chamber.
As the compressor is started in this state, the mixture liquid in the cylinder is discharged during the first rotation. The pressure established in the cylinder in the first stroking of the piston is not very high because the rotation speed is still low in this state. In the suction stroke of the next rotation, the liquid refrigerant residing just above the suction valve is sucked as the suction valve is opened. Since the piston moves in this state at a speed higher than that of the first rotation, the internal pressure of the cylinder is increased to an abnormally high level. This phenomenon lasts till the liquid refrigerant in the suction chamber is completely sucked and discharged. In consequence, the suction valve, cylinder head, discharge chamber, packing bearings and other parts are subjected to excessively large mechanical force. If this abnormal pressure increase takes place often, the concerned parts of the compressor may be broken due to fatigue, resulting in a shortened life of the compressor, as well as increased level of noise.
In addition, since the suction chamber is formed in the head cover, the suction chamber is overheated by the heat produced in the discharge chamber. In consequence, the refrigerant gas is heated just before entering the cylinder, resulting in an increase in the specific volume of the refrigerant gas, and a lowering of the volmetric efficiency of the compressor.
The specification of prior U.S. Pat. No. 3,817,661 discloses a motor compressor for air conditioner, in which the cylinder head of the compressor is provided with a silencing mechanism to eliminate the noise generated by the sucked refrigerant gas to improve the performance of the motor compressor. More specifically, in this motor compressor, the cylinder head is divided by an acoustic partition place into an upper chamber and a lower chamber which are communicated with each other by means of an orifice having a restricted passage. This lower chamber has a central discharge chamber around which is formed a suction chamber consisting of three sections communicated with one another through restricted passages.
The refrigerant gas flows into the closed housing through the return pipe and via a filter and comes into the upper chamber through the end of the suction pipe. As the gas is relieved into the upper chamber, it is allowed to expand so that a silencing effect is obtained. The refrigerant gas then flows into the chamber, in which it is further expanded to produce the silencing effect.
The suction chamber acting also as a silencer is formed in the head cover of the cylinder head and around the discharge chamber, also in the hermetic motor compressor of the type stated above.